1. Field of the Invention
The present invention relates to a millimeter wave oscillator using a fiber Bragg grating, and more particularly, to a millimeter wave oscillator using a fiber Bragg grating capable of producing a light source having two wavelengths in a certain phase relationship to generate a signal in a millimeter wave band having high frequencies.
2. Discussion of Related Art
In general, when a millimeter wave (more than several tens of GHz) is generated using two light sources, a phase correlation between the two light sources is low. Thus, when the beats occur, a phase noise is generated around the beat frequency. Therefore, in order to reduce such a phase noise, an electrical feedback circuit or an optical feedback circuit is arranged between the two light sources to provide a phase lock between the two light sources.
A laser injection locking system is disclosed, in U.S. Pat. No. 5,485,481 entitled “Fiber Grating Stabilized Diode Laser” by B. F. Ventrudo, et. al., in which with a phase modulated primary laser signal inserted into a secondary laser, when the frequency of the inserted signal approaches a free running frequency of the secondary laser, the signal of the primary laser captures an output of the secondary laser and an output spectrum of the secondary laser is fixed at the inserted frequency
In addition, Masahiro ogusu, et. al. propose that, using a distributed feedback (DFB) laser diode as a primary light source, signals are externally modulated by 7 to 30 GHz and inserted through an optical circulator into a Fabry-Perot laser diode where a mode is oscillated in a gap of the frequency difference of the millimeter wave (60 GHz). For the modulated primary light source signal, harmonic waves are generated at intervals of 30 GHz so that when two modes with a frequency difference corresponding to the millimeter frequency of Fabry-Perot diode modes approach frequencies of the harmonic waves, all of the Fabry-Perot diodes are fixed to the frequencies of the harmonic waves of the primary light source.
As described above, injection locking should be conducted between two light sources to reduce a phase noise, so that there is a need for complicated optical and electrical apparatuses such as a high frequency modulator.